1. Field of the Invention
The present invenion relates to a method for detecting radiation image. More particularly, the present invention relates to a method for detecting radiation image employing a combination of a stimulabale phosphor and photosensitive elements.
2. Description of Prior Art
For obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having an emulsion layer containing a photosensitive silver salt material and an intensifying screen.
As a method replacing the above-described radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for example, in U.S. Pat. No. 4,239,968, has been recently paid much attention. The radiation image recording and reproducing method involves steps of causing a stimulable phosphor to absorb radiation energy having passed through an object or having radiated from an object; exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to sequentially release the radiation energy stored in the stimulable phosphor as light emission (stimulated emission); photoelectrically detecting the emitted light to obtain an electric signal.
Heretofore, it has been proposed in the radiation image recording and reproducing method to detect a radiation image by using a radiation image storage panel (i.e., a stimulable phosphor sheet) containing a stimulable phosphor and photoelectrically reading out radiation energy stored in the panel with a read-out system. The radiation image storage panel employed in the method has a basic structure comprising a support and a phosphor layer provided on one surface of the support. Further, a transparent film is generally provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock.
In the read-out system, a photomultiplier is usually employed as a photosensor as disclosed in Japanese Patent Provisional Publication No. 56(1981)-11395, and on the light-receiving face of the photomultiplier a light guiding sheet for receiving the emission from the surface of the radiation image storage panel and guiding it to the photosensor is provided.
More in detail, a radiation which passed through an object or radiated from an object is absorbed by the phosphor layer of the radiation image storage panel, and a radiation image of the object is formed on the panel as a radiation energy-stored image. Subsequently, the panel carrying the energy-stored image is excited with an electromagnetic wave (stimulating rays) such as visible light or infrared rays in the image read-out system, to release the energy-stored image as light emission (stimulated emission). The stimulated emission is guided in the interior of the light guiding sheet and then photoelectrically detected with the photomultiplier to give an electric signal. The radiation image of the object is then reproduced from the electric signal.
In the above-described radiation image recording and reproducing method, a radiation image can be obtained with a sufficient amount of information by applying a radiation to an object at considerably smaller dose, as compared with the case of using the conventional radiography. Accordingly, this radiation image recording and reproducing method is of great value especially when the method is used for medical diagnosis.
Nevertheless, the above-mentioned radiation image recording and reproducing method has some problems. In the read-out operation, the radiation image storage panel is sequentially irradiated with a light beam (i.e., stimulating rays) having a small beam diameter such as a laser beam, namely, scanned with laser (main-scanning or sub-scanning), and the light emitted from the panel under the scanning is detected with a photosensor such as a photomultiplier to be converted to an electric signal. This read-out operation requires not a short period of time (several ten seconds). In order to detect the light which is sequentially emitted by each phosphor particle in the radiation image storage panel irradiated with the stimulating rays, the panel is usually transferred under the irradiation of stimulating rays (sub-scanning or main-scanning). Consequently, the detecting operation (read-out operation) of the radiation image recorded on the radiation image storage panel is complicated.
Further, in the case that a light guiding sheet is used in combination with the photomultiplier to efficiently detect the light emitted from the radiation image storage panel, the read-out system becomes more complicated and accordingly the operation sometimes encounters certain troubles.